Pour 1 1/2 cups of cream into a large metal mixing bowl and stash it in the freezer.
Place the chocolate,butter, and liqueur in another large metal bowl and melt over a pan of barely simmering water ,1 inch high, stirring constantly.
Remove from the heat while a few chunks are still visible. For the next 5 minutes, stir occasionally, until it cools to just above body temperature. Set aside.
Place the remaining cream in a small saucepan and sprinkle the gelatin over it. Allow the gelatin to bloom for 10 minutes, then dissolve the gelatin by gently haeting and swirling the pan over low heat. DO NOT LET THE CREAM BOIL, as this will affect the gelatin's setting power very badly.
Stir the above described into the cooled chocolate and set aside.
Remove the cream from the freezer and use a electric hand mixer to beat the cream to medium peaks.
Stir in a little whipped cream into the chocolate mixture. Then fold in half of the remaining whipped cream. Don't over beat the mixture or you'll ruin it. Then add the rest of the whipped cream and fold it in. Make sure it is light and fluffy, even with a few flecks of white.
Cover the bowl with plastic wrap and pop into the fridge for 2 hours.